Ignition device comprising a predetermined breaking point for the propelling charge of a gas generator associated with a passenger protection device in motor vehicles

ABSTRACT

The invention relates to an ignition device comprising a housing ( 2 ) in which an ignition chamber ( 4 ) for ignition material ( 5 ) is arranged. Said ignition chamber is covered with a flap ( 12 ), the bottom thereof having a predetermined breaking point. The breaking point ( 15 ) extends in an approximately S-shaped pull between opposite edges of the bottom ( 14 ). When the predetermined breaking point is broken by igniting the ignition material ( 5 ), parts ( 14   a,    14   b ) of the bottom ( 14 ) are bent upwards in such a way that the propulsion gases (T) of the ignition materials ( 5 ) are redirected by said parts ( 14   a    14   b ). Said construction enables the ignition device ( 1 ) to have a reduced height, and laterally-arranged propelling charges can be ignited in a reliable manner.

[0001] The invention relates to an ignition device for a propellant charge of the gas generator of a passenger protection device in a motor vehicle in accordance with the overall concept of patent claim 1. Passenger protection devices include, for example, collision protection cushions, so-called “airbags”, that arrest passenger movement during a collision, or belt tighteners that pull a safety belt tight during a collision.

[0002] Such an ignition device is known from the German Patent Publication DE-C1-197 33 353. This ignition device includes a housing with an ignition chamber in which an ignition material is positioned that is ignited electrically during a collision. The housing includes a cap that covers an ignition chamber with a sidewall and a bottom. The bottom is provided with a predetermined breaking point that includes linear sections formed by thinner material. A cross or star is stamped into the bottom of the cap, whereby the cross or star arms extend from the center of the bottom to its edges.

[0003] When the ignition material is ignited during a collision, the predetermined breaking points are broken by the propellant gases formed, and the bottom is bent into four or more flaps.

[0004] An electrical ignition device for a gas generator that includes a housing with an ignition chamber to hold the ignition material is known from the German Patent Publication DE-A1-44 29 178. The ignition chamber is covered by a cap that is a part of the housing. This cap includes recesses on its face that function as predetermined breaking points.

[0005] A similarly designed device, according to the German Patent Publication DE-A1-402 66 55, includes predetermined breaking points on the face of the cap covering an ignition chamber arranged as concentric circles.

[0006] In the ignition device for a gas generator according to the German Publication DE-A1-400 18 64, the cap covering an ignition chamber includes weakened areas on its sidewalls that function as predetermined breaking points.

[0007] In the ignition device disclosed in the U.S. Pat. No. 5,821,446, the cap covering an ignition chamber includes several weakened areas that define the predetermined breaking points.

[0008] The automobile industry prefers the smallest possible design for the gas generator of the passenger protection device, particularly when limited space is available, as is the case when the gas generator is built into the steering wheel with the airbag. The dimensions of the gas generator in the installation area of the ignition device are fixed, and have been made ever smaller in the course of time. The free spaces between the individual components are thus so small that they may hardly be matched to the dimensions of the bent flaps of the bottom during breakage of the predetermined breaking point. The flaps may then be only partially bent, so that difficulties may arise for smooth ignition of the propellant charge.

[0009] Further, for gas generators built into automobile steering wheels, the propellant charge for the collision cushions are positioned in a ring around the ignition device so that the propellant gases developed along the axial direction from the ignition material in the ignition device must be deflected to ignite the propellant charge for the collision cushions.

[0010] It is the principal objective of the invention to provide an ignition device of the type discussed above so that the gas generator may be short and so that ignition may result from laterally positioned propellant charges.

[0011] This objective is achieved according to the invention through the characteristics of Patent claim 1.

[0012] Accordingly, the predetermined breaking point is in an approximately S-shaped path or that of a double sickle between opposing edges of the bottom. The sections of the predetermined breaking point at the edges of the bottom preferably extend approximately parallel to each edge over a considerable portion of the circumference that preferably includes between one-quarter and one-eighth of the circumference. The sections of the predetermined breaking point between edges of the bottom preferably pass through the center point of the bottom.

[0013] When the predetermined breaking point ruptures according to the progression defined by the invention, the two areas at both sides of the predetermined breaking point symmetrical to the center point of the bottom are bent upward.

[0014] The shape thus formed is slightly similar to a fan blade.

[0015] This configuration has several advantages:

[0016] The two areas of the bottom at both sides of the section of the predetermined breaking point between the opposing edges no longer need to be bent to the extent that they allow the propellant gases to flow freely, as is the case with the above-mentioned conventional predetermined breaking point. In contrast to the known solutions, a large flow is enabled, even when the two sections are only slightly bent, that is greater than with the known predetermined breaking points under the same amount of bending. Thus, the height of the ignition device may be reduced so that the above-mentioned problems regarding installation dimensions may be solved.

[0017] Furthermore, through the oblique positioning of the two areas of the bottom divided by the predetermined breaking point, the propellant gases formed by the ignition material may also be deflected radially and laterally into the approximate shape of a fan stream, so that a propellant charge placed there will be reliably ignited.

[0018] According to an advantageous embodiment of the invention, the section of the predetermined breaking point is located between the edges of the bottom essentially along a straight line. A relatively sharp corner is preferably provided between this section and the sections of the predetermined breaking point extending essentially parallel to the edge of the bottom. Such a design allows manufacture using simple tools and reproducible bursting of the predetermined breaking point.

[0019] Further embodiments of the invention may be taken from the dependent claims.

[0020] The invention is described in more detail using illustrations, which show:

[0021]FIG. 1 a partially cutaway view of an ignition device according to the invention with a cap covering an ignition chamber in which a predetermined breaking point is provided;

[0022]FIG. 2 a top view of the cap showing the path of the predetermined breaking point;

[0023]FIG. 3 a side view of the cap which has burst at the predetermined breaking point; and

[0024]FIGS. 4 and 5 further views of the cap with varying paths of the predetermined breaking point.

[0025]FIG. 1 shows an ignition device 1 with a housing 2 in which a sleeve 3 is provided with an ignition chamber 4, which contains ignition material 5. Heads 6 of two contact pins 7 extend into the ignition material, and a resistance wire 8 is soldered between the heads 6. The contact pins 7 are held in a fit ring 9 whose interior is filled with molten glass 10 that has subsequently hardened. Another insulation layer 11 is provided between the glass ring 10 and the one on the ignition chamber 4.

[0026] A part of the housing 2 is a cap 12 surrounding the fit ring 9 and covering the ignition chamber 4 with the sleeve 3. The cap 12 includes a cylindrical sidewall 13 and a bottom 14 (exposed in the illustration).

[0027] The design described is merely an example; other designs of such ignition devices, of course, are conceivable in which only the ignition chamber is covered (see the aforementioned DE-A1-44 29 178).

[0028] The bottom 14 of the cap 12 is provided with a predetermined breaking point 15 that is created by stamping. The path of the predetermined breaking point 15 on the bottom 14 of the cap may be taken from FIG. 2. The path is S-shaped from the center to the edge, or in the shape of sickles with their handles abutting each other. The shape may also be referred to as a “double sickle”.

[0029] The predetermined breaking point includes a first section 15 a that extends between opposing points on the edge of the bottom 14 through the center point M in one stroke. A second or third section 15 b or 15 c is positioned at both endpoints of this section 15 a that extend in the same rotational direction and are approximately parallel to the edge of the bottom 14. The connecting points between the first section 15 a and the other two sections 15 b or 15 c are relatively sharp corners.

[0030] Sections 15 b and 15 c are limited by a sector extending from the center point M of the circle at a sector angle α that in this case is 90°. Naturally, other sector angles are possible that may be larger or smaller; this depends on the desired function of this predetermined breaking point 15.

[0031] By means of the illustrated separation, the bottom 14 is divided into two sections 14 a and 14 b that lie at both sides of the section 15 a of the predetermined breaking point. When melting of the resistance wire 8 ignites the ignition material 5, the propellant gases thus formed burst the predetermined breaking point 15 and bend the two sections 14 a and 14 b of the bottom 14 upward, as FIG. 3 shows schematically. FIG. 3 thus represents a view of the cap along projection P in FIG. 2.

[0032] The parts 14 a and 14 b are similar to a fan blade; their obliqueness caused by the propellant gases naturally depends on the amount of ignition material 5 provided in the ignition chamber 4. It can be seen that the propellant gases are deflected in the sections 14 a and 14 b, and also flow laterally from the cap 12 in a fan shape, as the arrow T in FIG. 3 shows.

[0033]FIG. 4 shows schematically a different path of a predetermined breaking point 15 on the bottom 14. This path is essentially similar to a written “S” and includes a lightly-deflected section 15 a that passes through the center point M of the bottom 14, and two sections 15 b and 15 c that are adjacent to this section 15 a, whereby a smooth transition is provided.

[0034]FIG. 5 shows a view of the bottom 14 of an essentially square cap with two different paths of a predetermined breaking point 15 or 15′.

[0035] The path of the predetermined breaking point 15 is shown with a solid line, and that of the predetermined breaking point 15′, with a broken line. The first area 15 a of the predetermined breaking point 15 passes through the center point M parallel to two opposing sidewalls of the cap 12. To its endpoints are connected angle-shaped sections 15 b or 15 c that extend parallel to the edge of the bottom 14. The angled sections each end at the height of the center point M so that each section covers approximately one fourth of the length of the edge of the bottom 14.

[0036] The first area 15′a of the second predetermined breaking point 15′ extends along a diagonal of the square bottom 14 through the center point M. The sections 15′b and 15′c connect to each end point, and each covers ⅛ of the edge of the bottom 14 and ends in FIG. 5 at the height of the center point M.

[0037] Even if in some examples the first section of the predetermined breaking point is shown and described as a straight line, it is clear that slight deviations from this are possible, such as a wavy or toothed path, etc. 

1. Ignition device for the propellant charge of a gas generator for a passenger protection device in an automobile, for example for an inflatable collision cushion or a seatbelt tightener, with a housing, an ignition chamber in the housing, and ignition material in the ignition chamber, wherein the housing includes a cap covering the ignition chamber having a side wall and a bottom, and with a predetermined breaking point provided in the bottom forming sections by reduction of material, characterized in that the predetermined breaking point (15) extends in one stroke in an approximately S-shape between opposite edges of the bottom (14).
 2. Ignition device as in claim 1, characterized in that the section (15 a) of the predetermined breaking point (15) between the edges of the bottom (14) passes through the center point (M) of the bottom (14).
 3. Ignition device as in claim 1 or 2, characterized in that the sections (15 b, 15 c) of the predetermined breaking point (15) extend along the edges of the bottom (14) approximately parallel to the edge of the bottom (14).
 4. Ignition device according to one of the previous claims, characterized in that the section (15 a) of the predetermined breaking point (15) between the edges of the bottom (14) essentially form a straight line.
 5. Ignition device according to one of the previous claims, characterized in that a relatively sharp corner (16) is provided between the sections (15 b, 15 c) of the predetermined breaking point (15) positioned along the edges of the bottom (14) and the section (15 a) between the edges of the bottom (14).
 6. Ignition device according to one of the previous claims, characterized in that the sections (15 b, 15 c) of the predetermined breaking point (15) along the edges of the bottom (14) pass through an arc of a circle with a sector angle α of at least 45° extending outward from the center point (M) of the bottom (14).
 7. Ignition device as in claim 6, characterized in that the sector angle is approximately 90°. 